Cooling systems for internal combustion engines in vehicles typically comprise a water jacket and various galleries in the internal combustion engine through which coolant, typically a mixture of water and ethylene glycol, is circulated. The coolant is heated by the engine and averages temperatures in the engine (which would otherwise vary significantly from place to place) and is then passed through a heat exchanger to dissipate waste heat to the surrounding atmosphere. After rejecting some heat through the heat exchanger, the coolant is returned to the engine for another cycle.
In addition to the water jacket, galleries and heat exchanger (typically in the form of a radiator), modern cooling systems often include a variety of other components such as heater cores, which are supplied with heated coolant to warm the interior of the vehicle, and lubrication oil and/or transmission oil coolers which are used to remove heat from the oils to enhance their operating lifetimes and/or performance.
Conventionally, these cooling systems typically consisted of one or two loops through which the coolant circulated with minimal control, other than a thermostat, which restricted the flow of coolant through the radiator until the engine had reached a desired operating temperature, and a control valve which would enable or disable the flow of coolant to the heater core depending upon whether it was desired to supply heat to the interior of the vehicle.
More sophisticated cooling systems, such as that taught in U.S. Pat. No. 6,668,764 to Henderson et al. have been proposed. The Henderson system is intended for use with diesel engines and employs a multiport valve in conjunction with an electrically operated coolant pump to provide a cooling system with several coolant circulation loops. By positioning the multiport valve in different positions and operating the electric water pump at different speeds/capacities, different functions can be performed by the cooling system. For example, at engine start up in cold ambient temperatures, all coolant flow through the engine can be inhibited. Once a minimum engine temperature is achieved, a flow of coolant can be provided to a passenger compartment heater core. Once a higher engine operating temperature has been achieved, or a specified temp has been exceeded, a flow of coolant can be provided to a lubrication oil heater core to assist the lubrication oil in achieving a desired minimum operating temperature, etc.
While the cooling system taught in Henderson provides operating advantages, it still suffers from some disadvantages in that it requires an electrically operated coolant pump with a relatively high capacity to meet worst case cooling conditions. In zero flow, or restricted flow, conditions the electric coolant pump must be electrically shut down as such pumps typically cannot be operated under zero flow conditions without damaging the pump. Further, such pumps are more expensive to manufacture, control and maintain than are mechanical coolant pumps and can be more subject to failures. Further, the cooling system taught in Henderson requires both a lubrication oil cooling heat exchanger and a lubrication oil heating heat exchanger to be able to raise the temperature of the lubricating oil of the engine to a desired minimum operating temperature and to then assist in cooling the lubricating oil.
It is desired to have a cooling system which provides for more sophisticated heating and cooling strategies without requiring electrically operated coolant circulation pumps or other expensive components.